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Aren't we ALL fat-burners and sugar-burners? What's the difference?

I'm hoping someone can explain something I've been confused about: What is the difference between a 'fat-burner' and a 'sugar-burner'?

This is my understanding, correct me where I'm wrong:

Even if someone is eating a high carb diet, as long as they are eating below their caloric maintenance requirement, the body will automatically switch over to burning stored fat (assuming it doesn't decide to suppress metabolism instead).

So, if there is a caloric deficit, then regardless of what macros the person is eating, the body will be burning fat, right?

A little background:

For a year, I ate a strict low-carb (about 75-125 grams/day from fruit+veggies), low-fat, high-protein paleo diet. Eating low carb was essential for me to eliminate binge-eating and food obsession. When I decided to add some good quality saturated fat for several months to my diet because I believe they are really important, I put on about 10lbs of fat. This made me realize that yes, eating fat DOES cause fat gain. During this time, I intermittent fasted regularly, with some days eating 1 huge meal, other days often skipping breakfast or eating in a 4-8 hour window. My appetite was easy to control, but I didn't lose that extra fat I gained.

In the past month, my new experiment has been to go back to low-fat, but dramatically increase my carbs in the form of starches (white rice, potatoes) and sugar (cane, honey) but no corn-syrup in any amount (this kept me from binging on junk food). I expected this would make my appetite go bananas, but surprisingly IT DIDN'T. Some days I ate fruit for breakfast and had some sugar in my tea, then wouldn't be hungry for lunch. Other days, I have been more hungry, but small snacks easily cured this problem. The only thing I noticed was that it was important to have a little more fat with dinner to make sure that I didn't have trouble sleeping due to low blood sugar issues in the middle of the night.

In theory, eating lots of starches and sugars should be causing a non-stop insulin response = fat gain, but I've not gained any extra fat eating this way. In fact, based on how my clothing fits, I seem to have actually lost a little bit.

This leads me to think that the whole sugar burner vs. fat burner idea is a bunch of nonsense.

Eating high fat keeps blood sugar stable, which means less hunger. That makes sense. But what doesn't make sense (unless I'm missing something) is how eating high fat can force the body to burn it faster or more efficiently. Clearly, this doesn't happen for me.

I'm hoping someone can explain this fat-burning concept to me, since eating fat for me has only led to storing fat.

Comment

I can't speak specifically to your situation as I am not aware of your specific metabolic intricacies.
I am not an expert on it by any means, but here's my take.

The primary factor in the fat burning story, as I understand it is that fat should be considered the primary fuel source for the body & glucose the secondary fuel source because of the often explained reasons, we store more fat than glucose, there is twice as much energy in the fat, the log & kindling analogy, the insulin reduced sensetivity issues with high carb consumption etc.
The other major factor I believe is liver load, as I understand it fat from digestion goes straight to the bloodstream and the tolerances for fatty acids in the blood are wider than those for glucose so we van have greater fluctuations of serum fatty acid levels without ill effect. Once the body cells have taken up what they need for metabolism then the excess is shunted to the adipose for storage, all this bypasses the liver, hence a high fat diet reduces liver load.
Conversley when glucose is absorbed into the bloodstream, it goes around the body and glycogen is restored, other cells take what they need, but it must be controlled within very strict limits, so as soon as the level rises even a little, then Insulin levels rise, blocking fat release from adipose tissue and putting the body into storage mode, then excess glucose goes to the liver to be processed into triglycerides then transported to adipose tissue for storage, usually a high carb diet will also contain fructose and this goes straight from the intestine to the liver to be converted to triglycerides.
So the problems with a high carb diet I see are:
1/ Glucose spikes more often and larger, high Glucose is corrosive to the body.
2/ Insulin spikes more often and larger, high Insulin is also corrosive to the body.
3/ Excess glucose must be processed by the liver, excess workload and this is often doubled by having fructose present at the same time in larger quantities.
4/ Long term this will lead to reduced Insulin sensitivity and a return to sugar cravings.

I think there is a fairly safe range in the vicinity of what Mark has outlined, but this is moderated by individual metabolic responses and the degree of activity, someone doing heavy workouts daily can tolerate much higher glucose loadings because their glycogen stores will sponge up most of the excess glucose, but the total carb loading should not be much greater than what the body can process for immediate needs and replenishing glycogen stores say over the 4 hour digestion time frame. Much more than that is pointless as it will get converted to fat and be stored anyway.

I think there is a slightly different response between men and women in regards to IF and likely diet as well so there may be a consideration there, not being sexist here, but as a general rule I think men form the Hunter mould better and women the Gatherer, and it is likely that women as gatherers really supplied the baseline food requirements, even if the men failed in the hunt, or never made it back at all, women could still provide for themselves & their children. I started some musing about this in another post recently as well, basically I believe bothe men and women would have minimum food availability on waking, then men would go hunt, women would gather, this would suggest women would start a bit of a light grazing process around late morning as they gathered small prey, insects, grubs, fruits, berries, tubers etc. so they would nibble some while they were collecting. I think this model fits well with what I have seen in the women I know, have read about here and a recent blog on Ketogenic Diet on Women & IF, more often than not women seem to feel more comfortable with the 16/8 protocol rather than the full 24 hour fast.
So if put this together and suggest women grazed in a longer eating window, then one could easily assume that their actual carb intake as a percentage was probably higher than men, but because it was only a little bit at a time, then it would not have caused high insulin levels as most of it would be used as they were gathering.

You may well feel fine now with the low fat diet, but if the carb intake is concentrated into specific regular meal times, my feeling is it will likely leed to all the normal responses expected from a low fat/high carb diet.

My feelings would be to keep any significant meals as low/moderate carb, but possibly allow small carb snacks between meals if that's the way you want to go, basically simulate something like the ancestral gatherer with some afternoon grazing leading up to a main meal that is mostly protein and fat biased.
Anyway still musing with that model.

"There are no short cuts to enlightenment, the journey is the destination, you have to walk this path alone"

Comment

I also think that how insulin sensitive you are comes into play. Personally I am a type II diabetic. I am very insulin sensitive and eat no more than 30 grams of carbs a day. For others you can eat a bit more. I have done low fat diets and lost weight but it came back. Again for me, low fat diets are not sustainable. And I am gluten intolerant so I eat only veggies and some nuts as carbs. Again, this is all me. Each person is a bit different. But I do agree that if you are causing insulin/glucose spikes eventually your body pays a price. I think that Omni may be on to something with his/her(?) musings but it takes experimentation to find what works best for your body. Buy a glucose meter. Take your blood sugar just before eating and one hour after eating. Your goal is no raise in blood sugar. Your personal insulin sensitivity will determine how many carbs you can eat while still feeling good, maintaining health and losing weight if that is a goal.

Comment

Yes. This. If you are not insulin resistant then yeah, no problem eating less and losing weight.

I crossed some kind of line into insulin resistance while I was hiking the Pacific Crest Trail, 3000 miles of backpacking. I lost weight the first 5 weeks or so, then I went through a brief period of starvation where I was eating less than some anorexics while hiking the High Sierra (I ran out of food), and became quite thin. But after that, I started slowly gaining weight despite hiking 30 miles a day and once I stopped the hiking I could no longer find a balance where I could exercise without triggering a level of hunger you would not believe, or reduce intake by itself to a level that stopped the weight gain. I could no longer find a sweet spot to let me lose weight of even to just stop gaining.

But there's another difference for fat-burning and sugar-burning, and that is the one where maybe there's nothing metabolically wrong with you, but can you run or cycle all day long without gels and bars? Of do you get faint and weak without food every few hours? You can probably lose weight, but maybe you don't quite have that metabolic flexibility for peak performance on a calorie deficit.

Comment

I don't believe that fat burning vs sugar burning is a bunch of nonsense. However, the potential benefits seem to be subject to much variation between individuals.

Timing of carb consumption is much more critical than timing of fat consumption for most people, so it's trickier to get right.

I do best focusing the bulk of my carb consumption in the evening after exercise, also eating just fat, protein and non-starchy veggies for breakfast, and a moderate amount of carbs with my lunch with plenty of fat and protein. I burn a lot of glycogen through activity, but the rest of the time I am relying on fat for energy more so than carbs. My immune system is much stronger for eating higher fat, and I find it easiest to lose weight when restricting carbs to 130-150 g a day from starch and vegetables (most of that being burnt during activity).

While I agree with a lot of Omni's analysis, I am not a natural grazer! I prefer to eat 2 or 3 large meals a day and not snacking. IF once a week is ideal for me. When I IF more frequently than that it lowers my basal metabolic rate.

Comment

guess what - every single person burns both fat and sugar every single day. or you'd be dead. it's bullshit - want to burn mostly fat? eat mostly fat. want to burn mostly sugar? eat mostly sugar. still impossible to burn solely one or the other.

But there's another difference for fat-burning and sugar-burning, and that is the one where maybe there's nothing metabolically wrong with you, but can you run or cycle all day long without gels and bars? Of do you get faint and weak without food every few hours? You can probably lose weight, but maybe you don't quite have that metabolic flexibility for peak performance on a calorie deficit.

Back when I was eating significantly higher levels of SAD type foods (processed seed oils, HFCS, etc), this was definitely me. But, I also had a very dysfunctional relationship with food, and I'm now thinking that likely had a lot to do with my constant food cravings/false hunger. In the past month, I had many mornings where I had tea with sugar, an apple or a banana, and 2 rice cakes with jam, then walked 3+ hours in high heat, and wasn't really hungry for lunch hours later. I'm finding that now I can still go as long as I need to without food, and it's not the end of the world. I'm not sure if the situation will change or remain like this, but for now, my body feels just fine burning sugar. This is what led me to try to figure out this sugar-burner/fat-burner mystery.

Comment

One, is that your intake of food creates a physiological shift to primarily burning fat for fuel. Yes, because you limit carbohydrate and eat more fat. This leads to upregulation of fat burning enzymes. The necessary things to turn fat to fuel.

Two, now that you are a fat burner your body can also utilize fat more efficiently during workouts. In fact you can utilize fat at higher levels of intensity and for longer periods than someone that is not fat adapted. This allows you to save your high octane fuel (glucose) for when it is really needed. That makes sense since we carry tens of thousands of calories of energy as fat, but only a couple thousand in glucose.

Comment

One, is that your intake of food creates a physiological shift to primarily burning fat for fuel. Yes, because you limit carbohydrate and eat more fat. This leads to upregulation of fat burning enzymes. The necessary things to turn fat to fuel.

Two, now that you are a fat burner your body can also utilize fat more efficiently during workouts. In fact you can utilize fat at higher levels of intensity and for longer periods than someone that is not fat adapted. This allows you to save your high octane fuel (glucose) for when it is really needed. That makes sense since we carry tens of thousands of calories of energy as fat, but only a couple thousand in glucose.

The upregulation makes sense, but my understanding is that glucose is used preferentially, meaning that it will be used up entirely before switching over to burning fat. I've never heard of glucose getting saved to be used later while burning fat in the meantime (unless I'm misunderstanding what you meant).

Comment

The upregulation makes sense, but my understanding is that glucose is used preferentially, meaning that it will be used up entirely before switching over to burning fat. I've never heard of glucose getting saved to be used later while burning fat in the meantime (unless I'm misunderstanding what you meant).

If you correct that when you are in 'surplus' for both glucose and fat, your body will use glucose preferentially. And the modern diet (>300g of glucose a day) is certainly going to put you into glucose burning mode.

But if your glucose intake is low (say ~50g/day) then your body preserves your scarce glucose stores for organs which *have* to run on glucose only, like parts of your brain. It also downshifts your metabolism to run in 'scarcity' mode (which makes it harder to lose weight, since your BEE or base-energy-expenditure goes down), and powers them from fat. This is why VLC people get cold hands and feet (reduced circulation to less essential bodily functions).

Comment

If you correct that when you are in 'surplus' for both glucose and fat, your body will use glucose preferentially. And the modern diet (>300g of glucose a day) is certainly going to put you into glucose burning mode.

But if your glucose intake is low (say ~50g/day) then your body preserves your scarce glucose stores for organs which *have* to run on glucose only, like parts of your brain. It also downshifts your metabolism to run in 'scarcity' mode (which makes it harder to lose weight, since your BEE or base-energy-expenditure goes down), and powers them from fat. This is why VLC people get cold hands and feet (reduced circulation to less essential bodily functions).

Brain runs on ketones just fine, and only a very small amount of the brain needs glucose, and only as much glucose as your body is fully capable of providing through gluconeogenesis. So only a tiny bit of carbs is useful to your brain and obtaining it from carbohydrates is optional.Your Brain On Ketones | Psychology Today

Female, 5'3", 50, Max squat: 202.5lbs. Max deadlift: 225 x 3.

Comment

If you correct that when you are in 'surplus' for both glucose and fat, your body will use glucose preferentially. And the modern diet (>300g of glucose a day) is certainly going to put you into glucose burning mode.

But if your glucose intake is low (say ~50g/day) then your body preserves your scarce glucose stores for organs which *have* to run on glucose only, like parts of your brain. It also downshifts your metabolism to run in 'scarcity' mode (which makes it harder to lose weight, since your BEE or base-energy-expenditure goes down), and powers them from fat. This is why VLC people get cold hands and feet (reduced circulation to less essential bodily functions).

Magicmerl I usually like your posts but this part "It also downshifts your metabolism to run in 'scarcity' mode (which makes it harder to lose weight, since your BEE or base-energy-expenditure goes down), and powers them from fat." Is fairly much bunk. Fact is that your BEE goes down on any caloric restricted diet. So anytime your attempting to lose weight this will happen.

The real difference is that your body will preferentially burn fats at higher and higher intensities rather than glucose to retain glucose for absolute necessities. That is part of the adaptation of "scarcity" mode...which I find is a positive event considering the much larger supply of fat substrate for energy in the human body.

Comment

The upregulation makes sense, but my understanding is that glucose is used preferentially, meaning that it will be used up entirely before switching over to burning fat. I've never heard of glucose getting saved to be used later while burning fat in the meantime (unless I'm misunderstanding what you meant).

Glucose is used preferentialy from the blood, not because it is a prefered fuel, but because it can be damaging if level goes too high.
Our bodies do burn both glucose and fats all the time in various quantities, the question remains as to what the ideal diet ratio is, my feelings are it is somewhere in the range of 3:1 Fats:Carbs, the reasons being we have limited storage capacity for glucose.

Glucose storage in body:
1 - Blood serum, very limited due to the strict control of high/low levels, so not really a storage depot.
2 - Muscle glycogen, +/- 400g, significant but restricted to muscle it is bound in, unavailable to the brain.
3 - Liver glycogen, +/- 120g, primarily reserved to maintain Serum levels and most likely specific for brain functions.
4 - Digestive tract, ???g, this is the only place that can carry a significant quantity of glucose in the form of complex carbs that can be absorbed at a slow enough rate to maintain a fairly constant flow of glucose to maintain serum levels and hence allow one to be a "sugar burner" until digestion is completed, say max 3-4 hours, which goes in with the normal hunger/craving cycles.

Considering any excess glucose/fructose will always be converted to fats by the liver, I doubt you could ever get past 50:50 on a normal 3 meal routine, even if you eliminated all fats from your diet completely. The only possibility would be if you did round the clock snacking to supply a fairly continuous supply of glucose to maintain serum levels on the slightly high side.

Remembering also that solouble fibre and resistant starches will be fermented by gut flora to release Short Chain fatty acids irrespective of whether you are high or low carb, I would say we are all predominantly fat burners, just a question of by how much.

"There are no short cuts to enlightenment, the journey is the destination, you have to walk this path alone"

Comment

I have a question regarding glucose...etc
While not wanting to be in total ketosis, I'm aiming for the carb curve Mark explains.
I'm typically aiming for somewhere between 70 to 150 (around 100 most days, up to 150 is very unusual) g of carbs.
But as I'm needing a lot of calories, I tend to consume quite a lot of protein along with my fats.
Would it therefore turn my body into a sugar burner ?

Young self-caring Paleo-eater from France.
(So please forgive the strange way I tend to express myself in your beautiful language )